1. Field of Invention
The present invention relates to a bonding pad structure and a method for fabricating the same. More particularly, the present invention relates to a bonding pad structure of a power device and a method for fabricating the same.
2. Description of Related Art
As chip integration increases, various semiconductor packages are used, such as chip scale package or multi-chip module. However, a leadframe is usually used for packaging a low pin count chip such as a power device.
FIG. 1 is a schematic, three-dimensional diagram of a conventional power device.
Referring to FIG. 1, a conventional power device is formed on a substrate 100.
The power device includes a source region 102, a gate 104, an insulating layer 106 surrounding the gate 104 and a drain region 108 opposite the source region 102 and the gate 104. A material of the insulating layer 106 is phosphosilicate glass (PSG). The source region 102 is a stack made of a titanium layer (not shown), a titanium nitride layer (not shown) and an aluminum-silicon-copper alloy layer (not shown); the drain region 108 comprises the same material as the substrate 100.
FIG. 2 is a schematic, cross-sectional diagram of a conventional bonding pad structure of a power device.
Referring to FIG. 2, an aluminum bonding pad layer 204 is formed on a surface 202a of a substrate 200. A surface 202b of the substrate 200 is grounded to reduce the thickness of the substrate 200 after the semiconductor manufacturing processes are completed. An under ball metallurgy (UBM) layer 214a is formed on a portion of the aluminum bonding pad layer 204 located in a bonding pad window 206. The under ball metallurgy layer 214a is made of a titanium layer 208a, a nickel layer 210a and a silver layer 212a; the layers are formed by sputtering.
An under ball metallurgy layer 214b is then formed on a portion of a surface 202b located in a bonding region 216, and it is made from a titanium layer 208b, a nickel layer 210b and a silver layer 212b. The layers are formed by sputtering.
In the power device mentioned above, the under ball metallurgy layer 214a, 214b are individually formed in their own formation processes; thus, the manufacturing processes become complex. It is difficult to reduce the manufacturing costs.
Electroless plating is another method to form the under ball metallurgy layers. Since the layers on the aluminum bonding pad layer are different from those on the bonding region, various conditions are possible for the electroless plating process. For example, the substrate should be dipped into an alkaline solution to form a nickel layer on the bonding region. The substrate is dipped into an acidic solution to form a nickel layer on the aluminum bonding pad layer. Again, the under ball metallurgy layers are still individually formed, so electroless plating also increases the manufacturing time and the manufacturing costs.
The invention provides a bonding pad structure and a method for fabricating the same. In the invention, under ball metallurgy layers over a bonding pad and a bonding region are simultaneously formed by electroless plating so that manufacturing processes are simplified and manufacturing costs are reduced. Furthermore, the under ball metallurgy layers can provide good bondability and solderability. Intermediate plated layers are located between the bonding region and the under ball metallurgy layer, as well as between the bonding pad and the under ball metallurgy layer, to improve adhesion between the under ball metallurgy layer and the metal bonding pad, and the under ball metallurgy layer and the bonding region.
The invention provides a bonding pad structure. A substrate having a first surface and a second surface is provided. A metal bonding pad and a bonding region are respectively located on the first surface and the second surface. Intermediate plated layers are located on the metal bonding pad and the bonding region. Under ball metallurgy layers are on each of the intermediate plated layers such that each of the under ball metallurgy layers comprises a first plated layer and a second plated layer.
The invention provides a method for fabricating a bonding pad structure. A substrate having a first surface and a second surface is provided. A metal bonding pad is formed on the first surface, and a bonding region is defined on the second region. Intermediate plated layers are simultaneously formed on the metal bonding pad and the bonding region by electroless plating. Then, under ball metallurgy layers are simultaneously formed on each of the intermediate plated layers by electroless plating in which each of the under ball metallurgy layers comprises a first plated layers and a second plated layer.
In the invention, the intermediate plated layers are formed simultaneously by electroless plating, and the under ball metallurgy layers are the same. By this invention, the manufacturing processes are simplified, and the manufacturing costs and the manufacturing time are both reduced.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.